1. Field of the Invention
The present invention generally relates to frame relay networks, and more particularly to a system and method for testing end-to-end connections of a virtual circuit across a frame relay network, without disrupting other user traffic being channeled across the same virtual circuit.
2. Discussion of the Related Art
Modem communications networks often include a number of paths or links that are interconnected to route voice, video, and data (hereinafter collectively referred to as "data") traffic from one location of the network to another. At each location, an interconnect node couples a plurality of source nodes and destination nodes to the network. In some cases, the sources and destinations are incorporated in a private line network that may include a series of offices connected together by leased-lines with switching facilities and transmission equipment owned and operated by the carrier or service provider and leased to the user. This type of network is conventionally referred to as a circuit-switching network. Accordingly, a source node of one office at one location of the network may transmit data to a destination node of a second office located at another location of the network through their respective switching facilities.
At any given location, a large number of source nodes may desire to communicate through their respective switching facilities, or interconnect node, to destination nodes at various other locations of the network, the data traffic from the various source nodes is first multiplexed through the source switching facility, then demultiplexed at the destination switching facility and finally delivered to the proper destination node. A variety of techniques for efficiently multiplexing data from multiple source nodes onto a single circuit of the network are presently employed in private line networks. For instance, time division multiplexing ("TDM") affords each source node full access to the allotted bandwidth of the circuit for a small amount of time. The circuit is divided into defined time segments, with each segment corresponding to a specific source node, to provide for the transfer of data from those source nodes, when called upon, through the network.
Other data communications systems, in contrast, have not been as successful employing multiplexing techniques to enhance network efficiency further. In particular, frame-relay networks offer far fewer alternatives than their circuit-switching network counterparts. Frame-relay networks are often referred to as packet-switching networks. Packet-switching networks, as opposed to circuit-switching networks, allow multiple users to share data network facilities and bandwidth rather than providing a specific amount of dedicated bandwidth to each user, as in TDM. Instead, packet switches divide bandwidth into connectionless, virtual circuits. As is known, virtual circuit bandwidth is consumed only when data are actually transmitted. Otherwise, the bandwidth is not used. In this way, packet-switching networks essentially mirror the operation of a statistical multiplexer (whereby multiple logical users share a single network access circuit).
One problem, however, with such traditional virtual circuits relates to the throughput efficiency in frame-relay and other packet-switching networks. For instance, a one-to-one correspondence exists between applications and frame-relay virtual circuits, there being no inherent mechanism in today's frame-relay standards for transporting end-to-end data management. Internet Engineering Task Force Request for Comments ("IETF RFC") 1490 "Multiprotocol Interconnect Over Frame Relay," herein incorporated by reference, provides the ability to multiplex protocols, but forces the equation of a protocol to a single logical channel on a given virtual circuit. Additionally, IETF RFC 1490 protocol headers must appear on every single frame transmitted over the circuit, without exception.
The circuit and method of related U.S. patent application Ser. No. 08/557,873, filed on Nov. 14, 1995, and entitled Circuit and Method for Multiplexing a Frame-Relay Virtual Circuit and Frame-Relay System Having Multiplexed Virtual Circuits discloses a system and method for providing end-to-end data management over a single frame-relay virtual circuit of the network. Briefly, the circuit of the system includes: (1) a logical channel creation circuit for designating a channel flag and first and second headers to be associated with frames relayed via first and second logical channels over the single frame-relay virtual circuit, respectively and (2) a multiplexer for associating frames of first and second data streams with the first and second logical channels, respectively, by inserting the channel flag and second header into each frame of the second data stream and the first header into only frames of the first data stream for which the associated flags match the channel flag, the first and second logical channels thereby allowed to be multiplexed over the single frame-relay virtual circuit, ones of the frames of the first data stream free of the first header to reduce an overhead of the multiplexing circuit. Judicious choice of the channel flag allows the first data stream to be relatively free of additional overhead, while the second data stream bears the bulk of the additional overhead.
In a preferred embodiment of the system disclosed therein, the multiplexing circuit is adapted to operate in a virtual secondary channel mode wherein the logical channel creation circuit designates the first and second logical channels as primary and secondary channels, respectively, the first data stream subject to a more stringent performance requirement than the second data stream. In the virtual secondary channel mode, the multiplexing circuit allows the single frame-relay virtual circuit to relay the secondary channel. The primary channel may be employed, for instance, to carry user traffic, while the secondary channel may be employed, for instance, to carry management traffic.
While the system and method of this prior frame-relay management system provides an effective way to multiplex logical communication channels across a single virtual circuit, further improvements are still desired. Namely, a manner of providing non-disruptive diagnostics across a single virtual circuit.